I have been trying to get rid of my Check Engine light for a year. The code that I am getting is the 0401 code that refers to the EGR system.

Car is a 96 Merc Sable.

I went to my mechanic who kept telling me a certain part was the problem and when I replaced that part and the light was still on he told me it was another part. Now I know he is not doing this to make money because I go buy the part and put it on by myself. But after replacing the whole EGR system or at least all the parts of it I still have the light which seems to also affect the cars power and sometimes just shuts off if you put it in park.

So far I have replaced the EGR solenoid ,EGR Valve and EGR (DPFE) Sensor and none of that helped.

I’ve had P0401 (INSUFFICIENT EGR flow) on several Taurusables. It’s pretty common, as is O0402 (EXCESSIVE EGR flow). Sometimes they appear together. The cure in each case was the replacement of the vacuum/electric gizmo that is bolted to the rear of the intake manifold. It’s about the size f a cell phone, and silver in color (on your year Sable). Have you replaced that one yet? It should have been his first guess. About $75 from Ford wholesale or $30 from O’Reilly’s. (I was surprised they stocked it, but that one was for an '01).

It sounds like that may be the DPFE sensor because that is the size of a cell phone. Does it have 2 hoses and one plug on it? If so yes that was replaced because according to the mechanic that’s what causes this 95% of the time.

I have checked the Vacuum lines for clogs or cracks and everything checks out ok. How would I check the EGR piping? By that I assume you meant the small tubes that are colored green and red. I don’t know how I would check/clean those.

Yup, that’s the one. Hmmm. It DOES cure it 95% of the time. Suggest you look at all the other plumbing. I don’t think there is any way to hook that sensor up wrong. The hoses are two different sizes IIRC, and the elec plug can only go one way.

All the parts in that report are new parts so I don’t know if testing them would help any.

One thing I am wondering though. When we changed out the DPFE sensor and put the new plastic one in we found that the hose for the DPFE sensor was too short so we went to our local Napa and got another vacuum hose but the opening was slightly smaller inside then the one on the DPFE sensor, a very small difference, it still fit but tightly.
Could that small amount of size make any difference?